1. Field of the Invention
The present invention relates to a method and an apparatus for the early recognition of ruptures when continuously casting steel using an oscillating mold constructed of copper plates. The method includes continuously and comparatively measuring operating parameters, for example, the temperature distribution with respect to location and time in the copper plates, and analyzing the obtained measurement results.
2. Description of the Related Art
Methods for the early recognition of ruptures in continuous casting of steel with an oscillating mold constructed of copper plates are thus far only known in the experimental stage and are based, for example, on thermoelements with tongues in the copper plates of the molds. The early recognition of ruptures is considered an important operating means in order to prevent the risks and work stoppages when ruptures of the strand shell occur which is still extremely sensitive, particularly when casting thin slabs with a speed of, for example, up to 6m/minute and beyond. In this method, irregularities in the temperature distribution in the copper plate are measured over the casting period, are analyzed and signals are derived from the results, wherein these signals have the purpose of serving as criteria for a rupture.
Because of the relatively high thermal capacity of the copper plates, the known method reacts with a significant time delay and, therefore, can be considered substantially safe only with severe limitations.
In accordance with another method, acceleration sensors are used in an attempt to detect rupture-relevant problems in the manner of movement with respect to three axes in space during the mold oscillation. This system is deficient because the measurements do not always clearly and with a high accuracy detect a rupture. Consequently, the measurement system triggers either erroneous alarms prior to a rupture or an alarm is indicated too late or not at all.
DE 24 15 224 C3 discloses a plate mold for slabs whose mold walls have cooling chambers which define limited cooling zones. Connected to the water supply and discharge lines of the long side walls of the mold are measurement units for determining the discharged thermal quantity or the cooling capacity. In addition, an average value of the cooling capacity of the cooling chambers is simultaneously formed in the measurement units, wherein the average value is supplied to an average forming unit which is capable of controlling the conicicity of the short side walls of the mold. Because of the measurement of the heat fluxes in the mold, an early recognition of ruptures cannot be carried out with satisfactory accuracy.
DE 41 17 073 C2 discloses a method of determining by means of a calorimetric measurement in a slab mold the integral and specific heat transport at each individual copper plate. A comparison of the specific heat fluxes from the copper plate side facing the steel to the water-cooled side especially of the short side walls of the mold with the heat fluxes of the two long side walls of the mold makes it possible to regulate the conicicity of the short side walls independently of the various selected casting parameters. This known apparatus also is not suitable for a substantially safe early recognition of an acute danger of rupture.
DE 195 29 931 C1 describes a plate mold for producing strands of steel, particularly thin slabs, wherein the long side walls have at least three cooling segments which are arranged next to one another and are independent of each other. Temperature sensors are arranged in the walls of the chambers facing the strand, wherein the temperature sensors determine at least the temperature differences between the individual chambers or zones. This document also does not disclose any suggestion for further developing these means for the determination of the temperature of areas of a mold and to utilize these means for an early recognition of ruptures.
Also known in the art are systems in which thermoelements integrated in the mold walls are used for observing the temperature changes and distribution over the casting period and for building up a rupture protection by forming difference values.
In addition, an acceleration measurement of the mold by means of at least three acceleration sensors on the mold is known in the art, wherein the measurements determine deviations in the mold movement, i.e, wobbling, as a criteria for ruptures.